Mercury is the closest planet to the Sun and the fastest planet in the solar system. That is why ancient Romans named Mercury after the speedy Roman god. It is also the second smallest planet (after Pluto) in the solar system. In fact, if Earth was hollow, almost eighteen Mercuries could fit into it! Because Mercury is very close to the Sun, it is extremely hot on the side facing the Sun. Mercury has some other unique features compared with other planets in the solar system such as a thin atmosphere, a wrinkled surface, and an iron core.

Thin Atmosphere

Mercury’s atmosphere is very thin. The atmosphere of Mercury is mainly made out of sodium. Mercury’s atmosphere is so thin because the gases that were there before all got boiled by the sun. The thin air does not trap heat very well. So, Mercury is actually not as hot as Venus. Part of Mercury’s surface can rise to 800°F and part of Mercury can go down to -300°F. This can happen because in the day time the Sun heats up Mercury’s surface quickly and at night time Mercury loses most of its heat. With no air and no clouds, Mercury’s weather is always the same, extremely hot in the day and extremely cold in the night.

Wrinkled Surface

The surface of Mercury, a lot like the moon’s surface, is full of craters or holes. That is why it is wrinkly. Scientists think craters were created by flying objects like meteoroids that hit Mercury’s surface. So many meteoroids hit Mercury and not Earth because Mercury has a very weak atmosphere and Earth has a strong atmosphere so it is less likely for a meteoroid to survive the friction of Earth’s atmosphere and hit Earth. Besides craters, there are long, rounded cliffs called scarps on Mercury’s surface. Scarps stand from 1,000 feet to 2 miles tall and run from 10 to more than 300 miles long. Scientists think Mercury’s hills and scarps formed when it cooled and shrank.

Huge Iron Core

Mercury’s core is one of the most interesting parts of Mercury. Here are some reasons why. Mercury’s core is made up of a large amount of iron. That is why Mercury is very dense and heavy compared with other planets. The core is surrounded by a layer of liquid material, and it is covered by a thin, rocky layer. It is still a mystery why Mercury has such a large iron core. One explanation is that Mercury crashed into another planet when it was very young and the two planets combined cores to create Mercury’s large core, but we could not know this for sure.

The reason why we know those unique features about Mercury is because men have been observing Mercury for a long time. In 1973, the United States sent a spacecraft called Mariner 10 to explore Mercury up close. Mariner 10 was so far the only spacecraft to explore Mercury and it made some very important discoveries. Here is some information on Mariner 10’s mission.

Mariner 10 took a lot of pictures of Mercury. Scientists learned about craters and scarps on Mercury’s surface. By sending radar waves from Mariner 10 to Mercury’s surface, the equipment on the spacecraft could tell if there were craters or scarps by measuring how fast the radar waves bounced back. Scientists also learned about Mercury’s other surface features and its atmosphere. In fact, Mariner 10’s mission found more information on Mercury in one year than we had discovered in about 5,000 years!

Mariner 10 was the first spacecraft to ever use gravity from another planet to get to another planet. When it flew very close to Venus, Venus’s gravity pull the spacecraft even closer and faster and then changed its direction toward Mercury. It was not easy to do, but in this way Mariner 10 save a lot of fuel to reach Mercury. Mariner 10 also used the Sun’s wind to get to Mercury. When the fuel ran low, Mariner 10 opened its solar panels like sails to catch the solar wind. It took Mariner 10 about 5 months to reach Mercury and it stayed near Mercury for about a year.

Mercury is a very small planet, but a very interesting one. Almost all we know about Mercury is from Mariner 10. Mercury has a thin atmosphere, wrinkly surface, and a large iron core. It is very hot in daytime and very cold at night. Mercury is one of the most unique planets in the solar system.